In industrial (or manufacturing) settings, such as for petroleum refining, data, measurement values, control signals, and the like are generally transferred between control systems and one or field devices (e.g., sensors or actuators), requiring a large number of interface circuits. The connection or input/output (I/O) pins for conventional interface circuits communicating with the industrial environment are typically designated in general, based on the function for the I/O pins. Generally, the function of an I/O pin is determined by the physical properties of the signal, upstream or downstream higher system functions, and the system configuration. The field devices present interfaces that generally fall into one of four input/output (I/O) function categories, Analog Input (AI), Digital Input (DI), Analog Output (AO), or Digital Output (DO).
Limitations of existing interface circuit implementations are numerous. Such interface circuits have served only single or a very limited number of I/O functions, and have sometimes required three or more wire connection sites (screw terminals) to satisfy a broad range of functions. Moreover, such interface circuits have required the user to make decisions at the time of making wiring connections about the nature of the field device, have required wiring changes (in the circuit) if the user changes the nature of the device to be controlled have not supported voltage input types, have not supported differential input types, and have not been able to distinguish current shorts to ground from normal operation.